data-ad-format="horizontal">



 
While you are here..

We have used advertising to support the site so it can remain free for everyone. However, advertising revenue is falling and I have always hated the ads. So, would you go to Patreon and become a patron of the site? When we reach the goal I will remove all advertising from the site.

Become a patron of the site at   patreon.com/mathopenref

Famous Geometers